How to avoid the deformation in CNC machining of aluminum

In CNC machining of aluminum, there are many causes of deformation of aluminum parts, which are related to the material, the shape, the cutters, the machining process and many more. In this article, we will introduce some effective methods to prevent the deformation of parts during aluminum machining.

How to avoid and reduce the deformation of parts in CNC machining of aluminum.

Here we have found six ways to minimize the deformation of aluminum parts during CNC machining.

1. Improve the cutting ability of the tool.

The material and geometrical parameters of the tool have a great influence on the cutting force and the heat of cutting. The correct selection of the tool is crucial to reduce the deformation of the workpiece.

– Front Angle: The front angle must be set correctly to maintain the strength of the blade, otherwise the sharp edge will be worn. Proper adjustment of the front angle can also reduce cutting deformation, ensure smooth chip evacuation, and reduce cutting force and temperature. Do not use tools with a negative rake angle.

– Rear angle: In rough milling, high feed rate, high cutting force and high heat mean that the tool must consider heat dissipation. Therefore, the back corner should be smaller. However, in precision milling, sharp edges are required to reduce friction between the side and the machined surface and elastic deformation. In these cases, the back corner should be larger.

– Bevel angle: To stabilize the milling and reduce the milling force, the bevel angle should be as large as possible.

– Main deflection angle: Appropriately reducing the main deflection angle can improve heat dissipation and reduce the average temperature of the machining area.

– Reduce the number of cutter teeth and increase the chip space. Due to the large plasticity of aluminum materials and the large cutting deformation during machining, a large chip space is required, so the radius of the bottom of the chipholder groove should be larger and the number of cutter teeth should be smaller.

– Precisely grind the cutter teeth. The roughness of the cutting edge of the cutter teeth should be less than Ra=0.4um. Before using a new tool, grind it before and after the cutter teeth to remove the remaining burrs and light serrations when sharpening the cutter teeth. In this way, the cutting heat can be reduced, and the cutting deformation is relatively small.

– Strict control of tool wear. After tool wear, the surface roughness of the workpiece increases, the cutting temperature increases, and the deformation of the workpiece increases. Therefore, in addition to selecting tool materials with good wear resistance, the tool wear standard should not exceed 0.2 mm, otherwise there is a risk of chip accumulation. During cutting, the temperature of the workpiece must not exceed 100 ℃ to avoid deformation.

2. Reduce the internal stress of the blank.

Natural or artificial aging and vibration treatment can partially eliminate the internal stress of the blank. Pre-machining is also an effective method. For large-sized blanks, the deformation after machining is also large due to the large clearance. If the excess part of the blank is machined in advance and the allowance of each part is reduced, not only the deformation of the subsequent process can be reduced, but also some of the internal stress can be relieved after the pre-machining has been carried out for a while.

3. Improve the clamping of workpieces.

For thin-walled aluminum workpieces with low rigidity, the following clamping methods can be used to reduce deformation:

– When the three-jaw self-centering chuck or the spring chuck is used to clamp in the radial direction for thin-walled bushing parts, the workpiece will inevitably deform as soon as it is released after machining. In this case, the method of axial face clamping with better rigidity should be used. To do this, locate the inner hole of the workpiece, make a threaded spindle, insert it into the inner hole of the workpiece, use a cover plate to compress the face, and then tighten the nut again. When machining the outer circle, the clamping deformation can be avoided, achieving satisfactory machining accuracy.

– When machining thin-walled sheet metal workpieces, it is better to choose vacuum suction cups to obtain uniformly distributed clamping force, and then use smaller cutting parameters for machining, which can well prevent deformation of the workpiece.

4. Suitable machining methods

– For parts with large machining clearance, symmetrical machining should be selected to achieve better heat dissipation and avoid heat concentration during machining.

– If the sheet metal part has multiple cavities, machining should be done in layers. Each layer should be machined as much as possible in all cavities at the same time, and then the next layer should be machined so that the parts can withstand a uniform force and deformation is reduced.

5. Milling process

Rough milling focuses on improving efficiency and striving for higher metal removal rate per unit time. In general, rough milling can be used where the excess materials on the surface of the blank are removed at the fastest speed and in the shortest time to form essentially the geometric contour required for the finishing operation. Precision machining requires high precision and quality, so it is better to mill in up-cut.

Among the three elements of cutting parameters, the undercut has a great influence on the cutting force. If the machining allowance is too large, the cutting force of a tool path will be too large, which will not only deform the parts, but also affect the rigidity of the machine tool spindle and reduce the service life of the tool. If we reduce the depth of undercut, the production efficiency will be greatly reduced. Reduce the depth of cut, increase the feed rate and cutting speed to reduce the cutting force and ensure efficiency.